Spectroscopic evidence of chiral Majorana modes in a quantum anomalous Hall insulator/superconductor heterostructure

Topological superconductors are considered the key to realize topological quantum computation. With the discovery of quantum anomalous Hall insulator (QAHI), it has been proposed that heterostructure of QAHI with conventional superconductor can be an ideal platform for obtaining Majorana fermion. By introducing superconductivity into dissipationless edge state of QAHI, two chiral Majorana edge modes with different Chern number N of 1 and 2, respectively, can be generated. Recently, He et al discovered the signature of integer and half-integer quantized conductance plateaus in QAHI/SC heterostructure. However, few arguments have indicated that there may be other mechanism to explain the phenomenon. Here we show spectroscopic evidence to support the existance of superconducting QAHI state at the edge of QAHI/SC heterostructure by using nano-point contact technique. Two different topological non-trivial phases are observed when the QAHI is gradually driven through its magnetization reversal. The N = ±1 phase with a conductance near 2e²/h occurs in a narrow field regime just before the QAHI enters a trivial insulating state. Our results are consistent with theoretical predictions and will help to confirm the previous result of half-integer quantization due to Majorana fermion.